Breech mechanism for automatic weapons



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United States Patent 3,153,982 BREECH MECHANISM FOR AUTOMATIC WEAPONS Paul Seifried, Oberweiler, Weilermatt, Badenweiler, Germany, assignor to Firma Rheinmetall G.m.b.H., Dusseldorf, Germany Filed Nov. 8, 1962, Ser. No. 236,232 14 Claims. (Cl. 89-194) The present invention relates to a breech mechanism for automatic fire arms forming an inertia operated mass breech mechanism, and having a breech head located at the rear end of the barrel, a breech body longitudinally displaceable relative to the breech head, accelerating means between breech head and breech body, and a coupling member, rotatably located in the breech body, having the shape of a lever, and locking breech head and breech body in the closing position of the breech mechanism, wherein the entire breech mechanism may move back under the action of the cartridge base pressure and is again advanced and moved into the closing position under the action of the resilient returning means.

In these automatic weapons, in which the breech mechanisms move back during the firing and are accelerated by throwing members in the axial direction, there occurs after the return of the breech mechanism during its impact on the rear end of the barrel or the locking member 21 more or less pronounced rebound.

In order to eliminate this effect, it has already been proposed to fit into these breech mechanisms a damping element whereby the kinetic rebound energy of the breech is destroyed by the impact on this damper. However, there remain always small rebound movements which are caused by the rebound of the damping element itself.

Also a locking ratchet loaded by a strong spring may be used to prevent the rebound of the breech members, provided that the spring force of the ratchet is stronger than the rebound energy of the breech mechanism.

However, in view of their inaccurate function, both these methods may be used only where the breech mechanisms have a sutficiently large locking and unlocking travel, or where the weapon is equipped with a mechanical striking mechanism, whereby ignition is delayed until even the smallest rebound movements have ceased.

Particularly with inertia operated mass breech mechanism-that is to say, mass breech mechanisms, in which the effective member has a comparatively small mass which is, however, subjected to a correspondingly high acceleration in order to obtain the required product of mass times acceleration, which decides the efiiciency of the breech mechanism-there occur frequent breakdowns because owing to the very short locking travel the rebound movements of the breech components are not terminated at the instant of the mechanical ignition. In weapons Without mechanical ignition retard it may easily happen that, owing to the rebound, the breech mechanism is open after the striking, causing fracture of the cartridge bases and considerable damage to the fire arm.

The present invention has the object of providing a breech mechanism, and more particularly an inertia operated mass breech mechanism for automatic fire arms, in which the rebound energy of the breech members is completely annihilated and undesired effects of the rebound no longer occur.

According to the invention, this object is realized by means of a breech mechanism in which the breech members are coupled by a ratchet or by a lever-like coupling. Instead of affecting the coupling by a strong spring force, as in known constructions, according to the invention, this spring force is replaced by a stronger dynamic force. According to this principle, there is located in the breech 3,153,982 Patented Got. 27, 1964 body, and effectively connected with the lever coupling, a longitudinally displaceable control mass, so dimensioned and arranged that it produces the locking force, absorbing the rebound energy of the breech body, as dynamic force. Since the locking force necessary to overcome the rebound energy need only be of short duration, this controlled dynamic force solves the task in a very favourable manner. The entire rebound energy of the breech afiecting the coupling and tending to open the same may be safely annihilated.

According to a further feature of the invention, the levershaped coupling is an accelerating coupling with an operating element which is stationary at the instant of impact of the breech head on the rear end of the barrel. The accelerating coupling and the operating element are so designed and arranged that the control mass receives during the time between the impact of the breech head on the rear barrel end and the impact of the breech body on the breech head, a motional component in the opposite direction to the direction of movement of the breech body. In this way, the control mass is decelerated relative to the breech body and impinges on the coupling with a lower velocity than the breech body on the breech head. In this way, on one hand, a part of the kinetic energy of the breech mechanism is deflected and can no longer affect the impact faces of the breech head, and on the other hand, with a suitable design of the accelerating coupling, a rebound of the control mass from the coupling is safely prevented.

By way of summary it may be said that, using the dis.- closure of the invention, a rebound safety may be pro vided, applicable to all breech mechanisms without restriction, and Without the uncontrollable after effects of a rebound mass or without being afiected by the braking effects of a spring operated ratchet.

According to the invention, the operating member for the accelerating coupling, for example, an inclined surface, cam, lug, release roller, or the like, is arranged on the rear part of the breech head. Thus, the operating member for the accelerating coupling is stationary at the moment of impact of the breech head on the barrel rear end, or during the time of the relative approach of the breech body towards the breech head, and ensures that the accelerating coupling is operated only during the last phase of the forward movement ofthe breech, causing the dynamic locking force to be generated and to be effective.

In order to lengthen the response travel of the accelerating coupling and to reduce the surface pressures as far as is possible, the lever end associated with the operating member has an inclined surface. Furthermore, also the surface of the control mass cooperating with the other lever end of the accelerating coupling forms an inclined surface, in order to increase the possible displacement of the control mass due to the pivoting movement of the coupling. For reasons of friction, it may also be convenient to provide two or more frictionless rollers on the pant of the control mass affected by the one lever end of the accelerating coupling and to form the lever end of the accelerating coupling acting thereon so that it presents an inclined surface.

In a further embodiment of the invention, the coupling surfaces of the coupling and the operating member or of the breech head effective in the locking position of the breech mechanism, are so designed that with the commencement of the recoil of the breech body under the action of the cartridge base pressure, the coupling also acts as accelerator, imparting an additional motional component to the control mass in the direction of movement of the breech body. Thus, according to this principle, the same elements by means of which the rebound energy of the breech is annihilated by producing an appropriate locking force, also the unlocking or opening acceleration of the entire breech is so affected that the inertia mass operated breech mechanism receives a double transmission and pure mass breech mechanisms receive a single intertia force, in addition to the rebound safety provided. structurally, this principle of the invention is applied in that way that the coupling surface of the operating member forms an inclined surface. Similarly, the coupling surface of the accelerating coupling is preferably inclined in order to reduce, as far as possible, the occurring surface pressures.

The advantages of the invention, both with simple and with transmission mass breech mechanisms, are obvious. With both mechanisms, the weight of the breech mass may be smaller, whilst maintaining the same performance. With controlled locked breech mechanisms with impact mass, the use of this rebound safety reduces the mass and maintains also here both advantages, namely lower weight and accurate rebound prevention. The importance of the lower weight is obvious, especially with automatic small arms, because in this case official weight restrictions must usually be observed. This saving in weight may then be used, for example, to reinforce other pants, such as the barrel.

Further details of the invention will become apparent from the following description, with reference to the accompanying drawings, in which:

FIGS. 1 and 2 are diagrammatic longitudinal crossseotions through the breech mechanism of the invention;

FIGS. 3 and 4 are diagrammatic longitudinal sections of a modified embodiment of the breech mechanism;

FIGS. 5 and 6 are diagrammatic longitudinal sections of a further embodiment showing the incorporation of the rebound safety with a simple mass breech mechanism.

The breech mechanism of FIGS. 1 to 4 is a inertia transmitted mass breech mechanism, comprising a breech head 1 and a breech body 2, displaceable longitudinally relative to one another through a control member 22. The accelerating means are two known support rollers, 3, resting against two inclined surfaces 4 of the body of the weapon, and causing, during the recoil of the head 1 during the firing, under the pressure exerted by the cartridge base, a rearward acceleration of the breech body 2 relative to the breech head 1. The rear end of the barrel is shown at 5, and the breech head 1 rests thereagainst in the closing position of the breech mechanism.

According to the invention, the breech body 2 is associated with a guide track 6, in which a control mass 7 may be longitudinally displaced against the force of a return spring 8. The forward part of the control mass 7 forms an inclined surface and cooperates with the rounded lever end 10 of a coupling 11, pivotably mounted in the forward part of the guide 6 of the body 2 by means of a pivot pin or axle pin 12 so that pivoting of this coupling 11 causes the longitudinal displacement of the control mass 7.

The front lever end 13 of the coupling forms a ratchet and has an inclined surface 14 and an inclined coupling face 15, cooperating with an inclined surface 16 and an inclined coupling surface 17 of a lug 18 mounted on the breech head, respectively. The incline 16 of the nose 18rising as viewed from the breech body 2,- forms the operating member for the coupling 11 during the forward travel of the breech, because the lever end 13 is moved thereby, with the axial approach of the breech body 2 towards the breech head 1, over its inclined surface in the upward direction. This causes the pivoting of the coupling 11. This position is shown in FIGURES 2 and 4, respectively. The inclined coupling surface 17 of the lug 18 is located in front of the inclined surface 16, and drops suddenly to form a locking chamber 19 behind the lug 18 of the breech head 1. On this, there engages with locked breech the corresponding inclined surface of the lever end 13. In this position, shown in 4 FIGURES 1 and 3, the coupling acts as locking device between breech body and breech head.

The breech body is permanently affected by the pressure of a resilient returning member, indicated in the FIGS. 1 and 2 embodiment by a helical spring 20, resting rearwardly against the weapon casing.

The embodiment of FIGS. 3 and 4 shows in this direction a slight modification in that there is provided, as returning means for the control mass 7 and as resilient returning means for the breech body 2, a common return spring 21, forming a rearward extension of the return spring 8 of FIGS. 1 and 2 and resting against the rear wall of the weapon casing.

The operation of the breech mechanism is as follows:

The forward movement of the breech components after the firing is effected as shown in FIGS. 2 and 4. During this entire forward movement of the breech components, up to the impact of the breech head 1 on the barrel rear end 5, the breech body 2 and the breech head 1 are kept at the same distance by the support rollers 3 which remain pushed inwardly during the forward travel by means of guide rails (not shown) and affect the control member 22 of the breech body 2 projecting into the breech head 1, as shown by the dotted lines. During this time, the inclined surfaces 16 of the breech head and 14 of the coupling 11 rest one on the other without movement, and the control mass 7 is at rest relative to the body 2. During the impact of the breech head 1 on the barrel rear end 5, the support rollers 3 may deflect, in front of the inclined surfaces 4 in the body of the weapon towards the outside under the pressure of the control member 22 of the body 2, opening the path for a further axial movement of the breech body 2 in the direction towards the breech head 1. During this further axial movement, the inclined surfaces 16 of the head 1 and 14 of the coupling 11 slide one on the other, resulting in a pivoting of the coupling 11 about the pivot 12, due to the rising incline of the surface 16. In consequence, the rounded end 10 presses on the inclined surface 9 of the control mass 7, causing an axial displacement of this mass towards the rear, relative to the breech body 2. Since the energy for carrying out this movement is taken from the kinetic energy of the forward movement of the body 2, this kinetic energy is positively reduced by an amount, corresponding to the accelerating effort or the kinetic energy of the control mass 7. The advance of the breech body 2 is therefore braked by deflecting this proportion of the energy.

By selecting suitably the angle of inclination of the inclined surfaces 14 and 16, the length of these surfaces, that is to say, by selecting the relative gap of movement between the breech head 1 and the breech body 2, further by selecting the angle of the inclined surface 9 of the control mass 7, that is to say, the translation ratio between the pivoting movement of the coupling 11 and the axial movement of this control mass 7, and also by the choice of the magnitude of this control mass, and with adapting these factors one to the others, the advance velocity of the control mass may be given a certain relationship to the advance velocity of the breech body 2, or, more exactly, the advance velocity of the control mass 7 may be retarded by a certain amount relative to that of the breech body 2.

Immediately before the breech mechanism reaches its closed position, that is, before the impact of the breech body 2 on the breech head 1, the two inclined surfaces 14 and 16 are disengaged and the pivoting movement of the coupling is terminated. Since no force is now acting on the forward lever end 15 of the coupling 11, the return spring 8, or 21, urging the control mass 7 forward, becomes effective, and causes through the inclined surface 9 of the control mass 7 acting on the lever end 10, a pivoting movement of the coupling 11 in the opposite sense so that the forward lever end 13 is pushed down. This forward lever end 13 may now engage into the locking chamber 19 in front of the lug 18 of the breech head 1, and its coupling surface may engage onto the coupling surface 17 of this lug. In this position, the coupling 11 acts as locking device, locking the breech body 2 with the breech head 1. During this engagement of the locking coupling, the control mass 7 is moved forward by the return spring 8, or 21, and presses, at the end of this forward movement with the entire energy produced by the return spring 8 or 21 on the coupling, and destroys the rebound energy of the breech body, affecting the coupling 11 through the surfaces 15, 17 and which would, without appropriate countering force, tend to open the coupling. The rebound of the control mass 7 from the coupling 11 is prevented by the delay of the advance velocity relative to the breech body 2.

During the recoil of the breech mechanism during the firing under the action of the cartridge base pressure, the breech body 2 is accelerated relative to the breech head 1 by the support rollers 3, as known per se. In consequence, there takes place between the forward lever end 13 and the lug 18 of the breech head a force causing, in view of the inclined position of the coupling faces 15 and 17, a pivoting movement of the coupling 11 about its pivot pin 12 during the relative rearward movement between breech body 2 and breech head 1. This causes the control mass 7 to be accelerated relative to the body 2, but this time in the direction of the breech body so that further kinetic energy is withdrawn from the rearward movement of the breech body or breech head. Thus, the effects of the accelerating means, comprising the support rollers 3, and this accelerating coupling, comprising the coupling 11, are uniformly directed and summated. Thus, there results during the recoil a considerable improvement of the known inertia mass breech mechanism.

If the breech body 2 and the breech head 1 are at a certain distance from one another, the coupling faces 15 and 17 are disengaged and the pivoting movement of the coupling is terminated. At this moment, the return spring 8, or 21, affects the control mass 7, causing the pivoting of the coupling in the opposite direction so that the inclined surfaces 16 and 14 are in engagement. In this position, shown in FIGS. 2 and 4, the breech assembly continues to recoil, until the parts are again pushed forward by the helical springs 20 or 21, respectively, and the breech head is seated on the barrel rear end 5.

FIGS. 5 and 6 show a simple mass breech mechanism, incorporating the rebound safety according to the invention. The breech mass 23 corresponds here to the breech body 2 and the control mass 7 is similar and slidable mounted in the breech mass 23, as in the embodiments of FIGS. 1-4. A substantial difference from the first embodiments is only that the inclined surface 14 on the forward lever end 13 points upwards. Instead of the nose 18 of the breech head 1 with the incline 16 and the coupling surface 17, the upper casing wall of the weapon has, near the barrel end 5, a lug 24 with corresponding inclined or coupling surface.

The operation of this rebound safety with the simple mass breech mechanism, is the same as described with the preceding embodiments according to FIGS. 1 to 4. because with all breeches shown, the nose 18 or 24 acting as operating member for the coupling 11, with the inclined surface 16 and the coupling surface 17 are stationary when the response travel is reached or opened. The control mass 7 is therefore always operated under the same conditions.

The incorporation of the rebound safety according to the invention in a simple mass breech mechanism has also the further advantage that, owing to the control mass 7, this breech becomes during the recoil of the breech mass 23 an inertia operated mass breech mechanism.

The invention is not restricted to the embodiments shown and described, and may be applied also to other breech mechanism. In addition, the individual components may have different configurations, without thereby departing from the principle of the invention. For eX- ample, there may be mounted on the part of the coupling 11 affected by the control mass 7, one or more anti-friction rolling bodies, the lever end cooperating therewith being preferably formed by an inclined surface. It is also possible to locate these non-friction bodies on the lever end 10, and to provide elements reducing friction also on the oblique surfaces 14 and 16 and on the coupling surfaces 15 or 17.

Furthermore, one or more return springs may be connected in parallel to the return spring 8 or 21 for the control mass 7, and these may be conveniently helical springs 25 mounted in cavities 27 of the breech body 2. They rest, on one side against the breech body 2 and on the other side against a nose 26 of the control mass 7, projecting into the cavity 27. This embodiment is shown by chain-dotted lines in FIG. 3.

What I claim is:

1. A breech mechanism for an automatic firearm having a rearwardly open barrel with a body and an opening therein arranged behind a rear end of said barrel, comprising a first part disposed behind the rear end of the barrel for obturating said rear end during firing, said first part being slidably guided in the opening of said body for a movement to and fro relative to the rear end of said barrel, spring means abutting said body of the fire arm and pressing said first part towards the rear end of the barrel, said first part being moved rearwards from the rear end of the barrel after firing by the action of the firing pressure and being moved again towards the rear end of the barrel by the action of said spring means, an element pivotably mounted in said first part and locking said first part if said first part is in its obturating position, means to cause said element to pivot during the last phase of movement of said first part towards the rear end of the barrel in its obturating position, a second part disposed in said first part and slidably guided for a reciprocating movement, said element having a portion engaging said second part and moving it rearwards when said element is pivoted during said last phase of said first part movement, said rearward movement of said second part during said last phase of said first part movement being directed substantially against the direction of said first part movement during said last phase, resilient means forcing said second part towards said element portion and forcing said element in a direction of its locking action.

2. A breech mechanism for an automatic fire arm having a rearwardly open barrel with a body and an opening therein arranged behind a rear end of said barrel, comprising a first part disposed behind the rear end of said barrel for obturating said rear end during firing, said first part being slidably guided in the opening of said body for a movement to and fro relative to said rear end of the barrel, spring means abutting said body of the fire arm and pressing said first part towards the rear end of said barrel, said first part being moved rearwards from said rear end of said barrel after firing by the action of the firing pressure and being moved again towards said rear end of said barrel by the action of said spring means, an element pivotably mounted in said first part to lock said first part if it is in its obturating position, first means to pivot said element during the last phase of movement of said first part towards the rear end of said barrel in its obturating position, second means to pivot said element during the first phase of movement of said first part away from the rear end of the barrel after firing, a second part disposed in said first part and slidably guided for a to and fro movement, said element having a portion engaging said second part and moving it rearwards when said element is pivoted by said first and said second means, resilient means pressing said second part towards said element portion and pressing said element in a direction of its locking action, said rearward movement of said second part during said last phase of said first part movement being directed substantially against the direction of said first part movement during said last phase, said second means pivoting said element being adapted to accelerate said second part relative to said first part during said first phase of movement of said first part.

3. A breech mechanism for an automatic fire arm having a rearwardly open barrel with a body and an opening therein arranged behind a rear end of said barrel, comprising a first part disposed behind the rear end of said barrel for obturating said rear end during firing, said first part being slidably guided in said opening of said body for a movement to and fro as to the rear end of said barrel, spring means abutting said body of the fire arm and forcing said first part towards the rear end of said barrel, said first part being moved rearwards from said rear end of said barrel after firing by the action of the firing pressure and being moved again towards the rear end of said barrel by the action of the spring means, an element pivotably mounted in said first part to lock said first part if it is in its obturating position, means to pivot said element during the last phase of movement of said first part towards the rear end of said barrel in its obturating position, a second part disposed in said first part and slidably guided for a to and fro movement, said element having a portion engaging said second part to move it rearwards if said element is rotated during the last phase of said part movement, said rearward movement of said second part during said last phase of said first part movement being directed substantially against the direction of said first part movement during said last phase, said spring means acting on said second part to press it towards said element portion and said element in direction of its locking action and pressing over said element said first part towards said rear end of said barrel.

4. A breech mechanism according to claim 3, in which resilient means are provided to abut said first part and press said second part towards said element portion.

5. A breech mechanism for an automatic fire arm having a rearwardly open barrel with a body and an opening therein arranged behind a rear end of said barrel, comprising a first member disposed behind the rear end of said barrel for obturating said rear end during firing, said first member being slidably guided in the opening of said body for movement to and fro relative to said rear end of said barrel, a second member disposed behind said first member slidably guided in the opening of said body for a movement to and fro relative to said first member, connecting means between said second member and said first member for a movement of said second member to and fro as to said first member over a certain distance from a close position to a spaced position and vice versa, spring means abutting said body of the fire arm and pressing said second member towards said first member and towards the rear end of said barrel, said first and second members being moved rearwards from said rear end of said barrel after firing by the action of the firing pressure and being moved again towards said rear end of said barrel by the action of said spring means, accelerating means to accelerate said second member relative to said first member from said close position to said spaced posi tion against the action of said spring means during the first phase of said rearward movement, a lever pivotably mounted in said second member and locking said second member with said first member in said close position of said first and second member, means to hold said first and second members in said spaced position after the action of said acceleration means until said first member is again abutting and again obturating said rear end of said barrel, means to rotate said lever during a relative movement of said second member towards said first member, a third member disposed in said second member and slidably guided for a to and fro movement,

said lever having an arm engaging said third member and moving it rearwards when said lever is rotated during said relative movement of said second member towards said first member, said rearward movement of said third member during said relative movement of said second member towards said first member being directed substantially against the direction of said relative movement of said second member, and resilient means pressing said third member towards said arm of said lever to force said lever in the direction of its locking action.

6. A breech mechanism according to claim 5, in which said means to pivot said lever is mounted on said first member.

7. A breech mechanism for an automatic fire arm having a rearwardly open barrel with a body and an opening in said body arranged behind a rear end of said barrel, comprising a first member disposed behind said rear end of said barrel for obturating said rear end during firing, said first member being slidably guided in the opening of said body for a movement to and fro as to the rear end of said barrel, spring means abutting said body of the fire arm and forcing said first member towards said rear end of said barrel, said first member being moved rearwards from said rear end of said barrel after firing by the action of the firing pressure and being moved again towards said rear end of said barrel by action of said spring means, a lever pivotably mounted in said first member, a stop mounted in said body to rotate said lever during the last phase of movement of said first member towards the rear end of said barrel in its obturating position, a second member disposed in said first member and slidably guided for a to and fro movement, said lever having an arm engaging said second member and moving it rearwards when said lever is rotated during said last phase of the movement of the first member, said rearward movement of said second member during said last phase of said first member movement being directed substantially against the direction of movement of said first member movement during said last phase, and resilient means forcing said second member towards said lever arm.

8. A breech mechanism according to claim 1, in which the element is a lever, havin a portion with an inclined surface, said means to pivot said element acting as a stop, and said inclined surface sliding over said stop.

9. A breech mechanism according to claim 1, in which said second part has an inclined surface to be engaged by said portion of said element, said portion forcing said inclined surface in substantially traverse direction.

10. A breech mechanism according to claim 1, in which said means to pivot said element acts as a stop having an inclined surface, and said element engaging said inclined surface.

11. A breech mechanism according to claim 2, in which said second means rotating said element acting as a stop having an inclined surface, and said element engaging said inclined surface.

12. A breech mechanism according to claim 2, in which said second means rotating said element acting as a stop, said element having an inclined surface engaging said stop.

13. A breech mechanism according to claim 5, in which means are provided for locking said first member in its obturating position, said locking means being active when said first and said second members are in said close position, and said locking means being released when said second member is moved away from said first member into said spaced position, and in which mechanical means are provided to move said first and said second members manually rearwards away from said rear end of said barrel, said mechanical means engaging said third memher and moving said third member away from said lever arm releasing said lever from the action of said resilient means whereby the locking action of said lever is re leased and said second member can be moved away from 10 said first member into said spaced position where said means whereby said locking action of said element is locking means of said first member is-released and said released and said first part can be moved away from said first member can be moved away from said rear end of real end 0f a d arr said barrel.

14. A breech mechanism according to claim 1, in which 5 References Cited the file of thls Patent mechanical means are provided to move said first part UNITED STATES PATENTS qg away from 'f e; end 2 Said 2,890,626 Amsler June 16, 1959 re sai mec anica means engaging sal secon part an moving said second part away from said element portion P S PATENTS to release said element from the action of said resilient 10 57 Great Brltaln Aug. 16, 1961 

1. A BREECH MECHANISM FOR AN AUTOMATIC FIREARM HAVING A REARWARDLY OPEN BARREL WITH A BODY AND AN OPENING THEREIN ARRANGED BEHIND A REAR END OF SAID BARREL, COMPRISING A FIRST PART DISPOSED BEHIND THE REAR END OF THE BARREL FOR OBTURATING SAID REAR END DURING FIRING, SAID FIRST PART BEING SLIDABLY GUIDED IN THE OPENING OF SAID BODY FOR A MOVEMENT TO AND FRO RELATIVE TO THE REAR END OF SAID BARREL, SPRING MEANS ABUTTING SAID BODY OF THE FIRE ARM AND PRESSING SAID FIRST PART TOWARDS THE REAR END OF THE BARREL, SAID FIRST PART BEING MOVED REARWARDS FROM THE REAR END OF THE BARREL AFTER FIRING BY THE ACTION OF THE FIRING PRESSURE AND BEING MOVED AGAIN TOWARDS THE REAR END OF THE BARREL BY THE ACTION OF SAID SPRING MEANS, AN ELEMENT PIVOTABLY MOUNTED IN SAID FIRST PART AND LOCKING SAID FIRST PART IF SAID FIRST PART IS IN ITS OBTURATING POSITION, MEANS TO CAUSE SAID ELEMENT TO PIVOT DURING THE LAST PHASE OF MOVEMENT OF SAID FIRST PART TOWARDS THE REAR END OF THE BARREL IN ITS OBTURATING POSITION, A SECOND PART DISPOSED IN SAID FIRST PART AND SLIDABLY GUIDED FOR A RECIPROCATING MOVEMENT, SAID ELEMENT HAVING A PORTION ENGAGING SAID SECOND PART AND MOVING IT REARWARDS WHEN SAID ELEMENT IS PIVOTED DURING SAID LAST PHASE OF SAID FIRST PART MOVEMENT, SAID REARWARD MOVEMENT OF SAID SECOND PART DURING SAID LAST PHASE OF SAID FIRST PART MOVEMENT BEING DIRECTED SUBSTANTIALLY AGAINST THE DIRECTION OF SAID FIRST PART MOVEMENT DURING SAID LAST PHASE, RESILIENT MEANS FORCING SAID SECOND PART TOWARDS SAID ELEMENT PORTION AND FORCING SAID ELEMENT IN A DIRECTION OF ITS LOCKING ACTION. 